1. Field of the Invention
The present invention relates to the use of gas discharge cells to couple driving circuitry to a gas discharge display/memory device.
2. Description of the Prior Art
In the prior art, multiple gas discharge display/memory panels have been proposed in the form of a pair of dielectric charge storage members which are backed by electrodes, the electrodes being so formed and oriented with respect to an ionizable gaseous medium as to define a plurality of discrete gas discharge units or cells. The cells have been defined by a surrounding or confining physical structure such as the walls of apertures in a perforated glass plate sandwiched between glass surfaces and they have been defined in an open space between glass or other dielectric backed with conductive electrode surfaces by appropriate choices of the gaseous medium, its pressure and the electrode geometry. In either structure, charges (electrons and ions) produced upon ionization of the gas volume of a selected discharge cell, when proper alternating operating voltages are applied between the opposed electrodes, are collected upon the surface of the dielectric at specifically defined locations. These charges constitute an electrical field opposing the electrical field which created them so as to reduce the voltage and terminate the discharge for the remainder of the cycle portion during which the discharge producing polarity remains applied. These collected charges aid an applied voltage of the polarity opposite that which created them in the initiation of a discharge by imposing a total voltage across the gas sufficient to again initiate a discharge and a collection of charges. This repetitive and alternating charge collection and ionization discharge constitutes an electrical memory.
In one form of panel construction, the electrodes are arranged in arrays, typically in parallel lines with the arrays of lines othogonally related, to define in the region of the projected intersections as viewed along the common perpendicular to each array a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Information can be stored and displayed by writing (initiating a discharge) at a selected location. For example, driving and addressing circuitry connected to the electrode arrays energizes a vertical electrode and a horizontal electrode which define the selected cell to generate a potential difference across the cell equal to or greater than the ignition potential of the gas. Such a method of addressing requires a separate addressing circuit for each electrode or a multiplexed addressing circuit in which a group of electrodes are connected to a common addressing circuit. Furthermore, a control circuit must be provided for selectively activating the desired addressing circuits. If selective erasing of the cells is also desired, additional circuitry is required to change the polarity of the addressing signal or change the timing so that the addressing voltage is in opposition to the sustainer voltage to develop a potential sufficient to cause a discharge in an "on state" cell and draw the charges from the dielectric surfaces such that the cell will be in the "off state".
An alternate form of addressing circuitry provides for a shifting of the information to be stored wherein the information is written in a designated portion of the panel and then shifted along the vertical and horizontal electrodes to the selected cells. The shifting addressing system is generally less expensive to manufacture, operate and repair than the above-described individual and multiplexing addressing circuits. A gas panel for use in selectively shifting information is disclosed in U.S. Pat. No. 3,795,908 issued to A. W. McDowell and F. M. Lay on Mar. 5, 1974. The panel includes a pair of orthogonally related electrode arrays arranged on opposite sides of an envelope filled with gas to define a matrix of individual gas discharge cells. An additional vertical electrode is provided along which information can be written by applying an addressing voltage between the additional vertical electrode and one or more horizontal electrodes which define cells only along the additional vertical electrode. Once the information has been written, it can be shifted into the matrix and along the vertical and horizontal electrodes.
The wall charge developed in the written cell spreads to adjacent cells to condition them. The conditioned cells can then be written by applying a shift voltage having a potential intermediate the sustainer voltage and the write voltage. The conditioned cells have a lower ignition voltage and are written when the shift voltage is applied whereas unconditioned cells remain in the "off state". Information can be shifted along the vertical or horizontal axes by applying a repetitive sequence of phased shift signals to sets of electrodes in the arrays. For example, if each set in an array includes three successively spaced electrodes and three phased shift signals are applied to respective electrodes of each set, the information will be shifted along an electrode of the other array in the direction of the order of the shift signals. When the information reaches the selected cell, the shift signals are removed and a sustainer signal maintains the selected cell in the "on state".
Another form of data shift panel is disclosed in U.S. Pat. No. 3,958,233 issued May 18, 1976 in the name of J. D. Schermerhorn. The driving circuitry includes at least three periodic potential sources with at least two of the sources being in phase with respect to each other and out of phase with respect to at least one of the remaining sources. A first set of spaced electrodes in one of the electrode arrays is connected to a first one of the potential sources; a second set of electrodes in the array is connected to a second one of the potential sources, each electrode of the second set being adjacent one of the electrodes of the first set; and a third set of electrodes in the array is connected to a third one of the potential sources, each electrode of the second set being intermediate an electrode of the first set and an electrode of the third set.
A further potential source is connected to at least one electrode of the other electrode array and combines with the two in phase potential sources to form a first composite wave form. The first wave form causes discharge sequences to occur at two adjacent discharge cells near the crosspoint vicinity of adjacent electrodes when at least one cell has been in a discharge state in an immediately preceding time interval or causes no discharge to occur at adjacent discharge cells when neither cell has been in a dischage state in an immediately preceding time interval or causes no discharge to occur at adjacent discharge cells when neither cell has been in a discharge state in an immediately preceding time interval. Another potential source which is out of phase with the in phase potential sources is connected to at least one electrode of the one electrode array wherein the further potential source combines with each out of phase potential source to form a second composite wave form which prohibits the continuance of a discharge at a cell near the crosspoint vicinity of an electrode connected to the out of phase potential source.
Therefore, the panel and driving circuitry disclosed in the patent No. 3,958,233 is arranged to maintain at least two discharge sites in a state of discharge during the shifting of such sites across a display and during the stable state, as opposed to the previously described prior art devices which utilize one discharge site for the stable state and two discharge sites in the on state only during the transitional periods incident to shifting a discharge site on the panel. Such a panel has a much better visual resolution of images because the spacing required for off state shift electrodes is reduced to a single electrode between information light spots on the panel face. If the electrodes of the other array are paired, four adjacent discharge sites can be maintained in the discharge state during shifting and during the stable state.
The information to be displayed is entered on a pilot electrode which is a pair of adjacent electrodes connected together at the input ends. A transfer electrode is positioned intermediate the pilot electrode and the first electrode of the one electrode array to transfer the input data to the array electrode so that it can be shifted to the desired position. The electrodes of the other array are extended into proximity with the pilot electrode so that input data can be positioned along the pilot electrode by pulsing the electrode along which the data is to be shifted.
Although both of the above-described gas discharge display/memory devices feature gas discharge coupling of the input data to the panel, the shifting and sustaining voltage circuits are directly connected to the panel electrodes. The present invention reduces the number of connections between the panel electrodes and the driving circuitry by utilizing gas discharge cell coupling.